The invention generally relates to hermetic compressors and more particularly to positive displacement oil pumps for hermetic compressors.
Oil pumps of various types are typically employed in hermetic compressors to provide sufficient lubrication to a multitude of interfacing bearing surfaces within the compressor. These types of pumps may be, for example, impeller pumps, centrifugal pumps or positive displacement pumps, the present invention related to the lattermost type. Positive displacement pumps are considered by many in the field to be the preferred type of pump for compressor applications, in part for the reason that these pumps can generate higher oil pressure than other types of pumps.
Previous positive displacement pumps include designs which cannot effectively be interchanged between compressor applications which have crankshafts which rotate in opposite directions, or in compressor applications having a reversibly rotating crankshaft. Such a pump design is intended to pump lubrication to the various interfacing bearing surfaces of a compressor only when the compressor crankshaft is rotating in a single, given direction.
Many compressors driven by an electric motor are intended to rotate only in a single direction (referred to hereinbelow as "unidirectionally-rotating"), but may, due to miswiring of the electric motor during assembly, be caused to run in a reverse direction. Under such circumstances, some previous, unidirectionally-rotating positive displacement pumps will not operate to provide lubrication to the interfacing bearing surfaces, and the compressor may seize or experience excessive wear during the reverse rotation.
Further, many unidirectionally-rotating compressors are subject to unintended reverse rotation upon shutdown of the compressor, as discharge pressure gases within the compressor, or within the refrigerant system into which the compressor is incorporated, expand through the compression mechanism thereof. This phenomenon is well known, particularly in scroll compressors. As discharge gases expand on shutdown of the compressor, they backflow into the discharge port of the interleaved scroll wraps, and cause the orbiting scroll to orbit in the direction opposite that in which the gases were initially compressed. Thus, on shut down, the compressor may behave like an expansion motor, the compressed gases causing rotation of the crankshaft in a direction opposite that in which the electric motor drives the shaft. Objectionable noise and vibration usually accompany such reverse rotation of the orbiting scroll, and are well known problems. Much effort has been made to prevent of reverse rotation of the orbiting scroll; these efforts may, for example, include the provision of check valves over the discharge port to prevent reversely flowing discharge gases from reentering the space between the interleaved scroll wraps. Indeed, a scroll compressor embodiment described hereinbelow includes such a check valve. Where reverse rotation of a compressor having a previous, unidirectionally operable positive displacement pump is not entirely prevented, however, sufficient lubrication to the interfacing bearing surfaces of the compressor may not be achieved during the period of reverse rotation. During such reverse rotation, even for brief periods on shutdown of the compressor, the interfacing bearing surfaces, which remain in sliding contact with each other, may not be provided with adequate lubrication, and may be subject to excessive wear or seizure.
Moreover, in some unidirectionally-rotating compressors, during periods of brief power interruption during which the compressor is caused to be reversely rotated by expanding discharge gases, the compressor may continue rotation in the reverse direction, driven by the motor, if power is restored to the motor while the compressor is still reversely rotating under influence of the expanding discharge gases. In such situations, the compressor may run in the reverse direction for quite some time and, if no provision is made for pumping lubricant to its interfacing bearing surfaces during reverse rotation, the compressor will likely seize.
Positive displacement pumps are often at least partially submerged in the oil located in the oil sump provided in the lower portion of the compressor housing, and are driven by the rotating crankshaft coupled to the rotor of the electric motor, the end of the shaft disposed in, and rotatable relative to a pump body. Oil is forced by the pump through an axial passageway provided through the crankshaft, the passageway in fluid communication with points of lubrication in the compression mechanism. In previous pumps, a radially-extending passage communicating with the axial oil passageway in the crankshaft is provided to lubricate the interface between the shaft and the pump body. The pump body may, in some compressors, also serve as a bearing which rotatably and/or axially supports the shaft relative to the compressor housing. Here, too, a radially-extending passage communicating with the axial oil passageway in the crankshaft is provided to lubricate the interface between the shaft and the pump body. The tolerance between the peripheral surface of the crankshaft and the pump body must be held to rather close tolerances, and the provision of the radially-extending passage requires additional machining and cost.
A positive displacement pump which provides lubrication to the interfacing bearing surfaces of a compressor which rotates in two directions, whether by design (hereinafter referred to as "bidirectionally-rotating") or a unidirectionally-rotating compressor caused to rotate in the reverse direction due to reexpansion of discharge gases, miswiring of the motor or a brief power interruption as described above, is highly desirable.
Further, a means of accommodating tolerances between the crankshaft and pump body of a compressor, and providing lubrication between the crankshaft and the pump body and/or a crankshaft-supporting bearing which comprises a pump body without requiring the additional machining associated with a radially-extending oil passage in the shaft, is also highly desirable.